BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #15

*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********


...THURSDAY MAY 28 2020 1:28 PM EDT...

Even though the Atlantic hurricane season does not start until June 1...continuing daily birdseye view posts on the Atlantic tropics due two areas of interest for tropical development...see area of interest sections below for additional details. Elsewhere...Tropical Storm Bertha has dissipated into a remnant tropical low pressure now located well-inland over the Ohio Valley region of the United States...see remnants of Bertha section for more information.


REMNANTS OF BERTHA...After making landfall on the South Carolina coast as a tropical storm 24 hours ago...Bertha has hightailed it quickly north-northwestard across the eastern United States and is already in the Ohio Valley region this morning while centered over eastern Ohio. This is because Bertha is embedded in strong deep-layered southerly flow between a persistent central United States frontal system off to the west and western Atlantic surface ridge and longwave upper ridge axis just to the east. The remnant low pressure resembled a tropical entity while the upper ridge axis supplied it with anticyclonic outflow supporting continued shower and thunderstorm activity...and on satellite and radar Bertha maintained a distinct cloud swirl with a comma shaped shower and thunderstorm mass. But as Bertha approaches Lake Erie and southeastern Canada...it is losing its distinction on all detection methods out ahead of an approaching upper trough and surface frontal system originating from western Canada. Bertha's remnant is expected to in fact lose its identity within the next 24 hours while overrun by the much larger surface low pressure field of the approaching cold front. The flood potential from Bertha is diminished as radar show less precipitation intensity and whatever is left of the circulation is moving quickly...which diminishes the amount of time for rainfall at a given location. This is my final statement on Bertha as it is no longer a tropical cyclone.


AREA OF INTEREST #1...An upper trough in the western Atlantic to the north of the Caribbean and southeast of Bermuda continues to amplify while a longwave upper ridge over eastern North America is finally beginning to shift into the northwest Atlantic and press against the upper trough. The eastern divergence zone of this upper trough is producing a large comma shaped shower and thunderstorm mass...as well as a new lengthy surface trough of low pressure. Over the next 24 hours this upper trough is expected to amplify further into an upper vortex while the upper ridge settles directly to the north. As this occurs...the upper vortex will produce an upper divergence maximum on its east side...resulting in a surface low pressure forming along the surface trough. The surface low is expected to form where water temperatuers are currently running at 24 to 26 deg C...at or just below the threshold for tropical development. However the forecast upper vortex is expected to be cold enough where it can help boost thunderstorm activity...therefore the forecast surface low pressure could acquire tropical characteristics and become a subtropical cyclone. I retain short-term 0% odds of subtropical development thorugh May 29 as the latest presentation of the upper vortex in the GFS model shows the vortex still being elongated and titled southwest-to-northeast such that wind shear may still be too high for any kind of tropical development through that timeframe. Peak odds of development are shown in my latest outlook to be at 48 hours when the upper vortex is shown to be more circular and the surface low pressure is shown in models to be more mature. My peaks odds of development are still on the low side...at 20%...at this time because the robust upper ridge with its east convergence will maintain a strong surface ridge in the western Atlantic...perhaps strong enough to make it more difficult for a surface low pressure to take hold...and in fact many in the latest suite of computer model runs show only a weak surface low pressure developing. Regarding track...the upper vortex and surface low pressure are expected to shift northwest and then north around the south and west sides of the upper ridge passing to the north. By 72 hours I drop the odds of development to a very small 5% as the track will take this system to water temperatures in the low 20s of deg C...and the upper vortex by that time will at the 200 mb layer be at 1215 dekameters above sea level (would like to see the upper vortex be at 1200 or less at those water temperatures to believe the upper vortex is cold enough to support thunderstorm activity). By 96 hours...development should no longer be possible with even cooler water temperatures...and as the system at the surface and upper levels should become abosrbed by what is now a vigorous upper trough and surface frontal system over central Canada.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z May 29)...0% chance of subtropical cyclone formation (western Atlantic near 28N-57W)

IOH 48 Hr Outlook (1200Z May 30)...20% chance of subtropical cyclone formation (western Atlnatic near 29N-57.5W)

IOH 72 Hr Outlook (1200Z May 31)...5% chance of subtropical cyclone formation (western Atlantic near 35N-57.5W)

IOH 96 Hr Outlook (1200Z Jun 1)...0% chance of subtropical cyclone formation (western Atlantic south of Newfoundland near 41N-55W)


AREA OF INTEREST #2...The thunderstorm activity in the eastern Pacific Ocean...to the southwest of Central America and south of southeastern Mexico...has reduced as the upper ridge/outflow in the region has become suppressed by the southward shift of the large upper vortex over the central United States. This could also be why a surface tropical wave passing through the region...at 92.5W...is inactive. Meanwhile a cluster of thunderstorms with some light rotation has developed just east of Nicaragua where the outflow of the upper ridge is curently maximum as this region is further away from the central United States upper vortex. The surface ridge weakness caused by the upper vortex's surface frontal system is too far north to pull the feature east of Nicaragua northward and keep it over water...thus a slow westward drift into Nicaragua is likely and tropical cyclone development here may not occur...although will continue to keep an eye on this feature. In 48+ hours...the upper vortex is expected to retrograde westward and away under the influence of a longwave upper ridge to build over western North America...which will allow the upper ridge/outflow in the eastern Pacific to re-expand and also reach western Caribbean-Central America-southeastern Mexico region of the Atlantic basin. During this time....computer models still favor developing a tropical cyclone in the eastern Pacific from this upper air pattern. In the longer range...toward the end of the 120-hour forecast period...models have largely abaondoned the idea of an Atlantic side tropical cyclone developing with the exception of the CMC....which brings the eastern Pacific tropical cyclone across central America and into the western Caribbean and then intensifies it significantly in the western Caribbean. However the CMC is usually overly-aggressive...so not taking this solution seriously at this time. For now...continuing an area of interest window over Honduras and the western Caribbean Sea. I only slowly raise odds of development at 72+ hours as any surface low pressure area that forms on the Atlantic side will be large/broad due to the large size of the upper ridge...thus likely taking time to develop into an Atlantic-side tropical cyclone if this were to occurr. I do not raise odds above 10% at this time due to most of the current model runs that do not develop an Atlantic-side tropical cyclone.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z May 29)...0% chance of tropical cyclone formation (Honduras near 15N-87W)

IOH 48 Hr Outlook (1200Z May 30)...0% chance of tropical cyclone formation (Honduras near 15N-87W)

IOH 72 Hr Outlook (1200Z May 31)...5% chance of tropical cyclone formation (north coast of Honduras near 16N-87W)

IOH 96 Hr Outlook (1200Z Jun 1)...10% chance of tropical cyclone formation (western Caribbean Sea near 16.5N-87W)

IOH 120 Hr Outlook (1200Z Jun 2)...10% chance of tropical cyclone formation (western Caribbean Sea near 16.5N-87W)

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